The present disclosure herein relates to semiconductor memory devices, and more particularly, to a flash memory device and a read method thereof.
Semiconductor memory devices are generally classified into volatile memory devices (e.g., DRAMs and SRAMs) and nonvolatile memory devices (e.g., EEPROMs, FRAMs, PRAMs, MRAMs, and flash memories). A volatile memory device loses data stored therein when power supply thereto is interrupted; whereas a nonvolatile memory device retains data stored therein even when power supply thereto is interrupted. In particular, a flash memory device is widely used as a storage medium in a computer system because of its high program speed, low power consumption and large data storage capacity.
In the flash memory device, data states storable in each memory cell may be determined according to the number of bits stored in the memory cell. A memory cell storing 1-bit data per cell is called a single-bit cell or a single-level cell (SLC), and a memory cell storing multi-bit data (i.e., at least 2-bit data) per cell is called a multi-bit cell, a multi-level cell (MLC) or a multi-state cell. The multi-bit cell is advantageous for high integration. However, as the number of bits programmed in each memory cell increases, the reliability decreases and the read failure rate increases.